Circuit for heat treating metallic objects



P 21, 1954 .1. A. REDMOND ETAL 2,689,900

CIRCUIT FOR HEAT TREATING METALLIC OBJECTS Filed May 5, 1950 High Q 1 Frequency Source High Frequency Source mum]: 30

I WITNESSES: INVENTORS John ARedmondond M W l ATTORNEY Patented Sept. 21, 1954 CIRCUIT FOR HEAT TREATING METALLIC OBJECTS John A. Redmond and William L. Corteggiano,

Baltimore, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 5, 1950, Serial No. 160,116

1 Claim. 1

Our invention relates to multiple frequency heat treatment of metallic objects and, in particular, relates to heat-treatment apparatus of the type that requires but a single heating unit.

In accordance with the prior art of which we are aware, the satisfactory heat treatment of metallic objects, such as gears, required relatively complicated work-handling equipment to move the gears undergoing heat treatment from the individual heating unit in which the low frequency preheat treatment was being applied to the individual heating unit in which the high frequency hardening treatment was being applied. Further, the apparatus of the prior art, when used for the heat treatment of gears having different physical dimensions, requires the use of an individual heatin unit with its respective power supply for each gear size treated. Such apparatus, while satisfactory for heat treatment of large quantities of like gears at a high rate, in certain situations proves excessively costly and difficult to maintain.

It is, accordingly, an object of this invention to provide apparatus for heat treating metallic objects by the application of multiple frequency currents in which said objects need not be moved from one heat-treatment apparatus to another.

Another object of this invention is to provide apparatus for heat treating metallic objects by the application of first a low frequency preheat: ing current and subsequently a high frequency hardening current, in which the said objects need not change position from one apparatus to another.

A further object is to provide a heat treatment apparatu which requires less electrical equipment and is more simple in operation than the prior art apparatus.

Still another object is to avoid the use of separate preheat inductor coils and their associated transformers and network apparatus.

A still further object is to provide apparatusfor applying multiple frequency energy to a gear undergoing heat treatmentin such a manner that said gear occupies but a single induction coil, and heat treatment energy of only one frequency is applied to said gear during a given time interval.

Anancillary object of this invention is to vary the actual power input to the gear undergoing heat treatment while the output of the power source to the heat treatment apparatus remains substantially constant.

Another ancillary object is to vary the power input to the metallic object undergoing heat treatment in accordance with the physical dimensions of said object.

The apparatus constructed in accordance with our invention allows the satisfactory heat treatment of metallic gears in but a single induction heating coil by the successive application of first a low frequency preheating current and subsequently a high frequency hardening current. An adjustable inductor in conjunction with a tapped output transformer allows the high frequency power input to the gear to be varied in accordance with the different sized. gears undergoing heat treatment and the requirements thereof for the desired hardening and at the same time maintaining a constant circuit inductance. Another adjustable inductor allows the low frequency power applied to the gear undergoing heat treatment to be varied in a similar man ner. First and third interlocked switches are ;provided, so the first switch, which energizes the induction heating coil with low frequency preheating current, is closed only when the third switch, which energizes the induction heating coil with high frequency hardening current, is open. A second switch allows the low frequency preheating voltage to be varied from a maximum to a minimum.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claim. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure 1 is a schematic diagram of our multiple frequency heat treatment apparatus showing the switching arrangement respectively between the low frequency and the high frequency power sources, and the variable impedances which are used to vary the power input to a metallic object undergoing heat treatment in the single induction heating coil.

Fig. 2' is a schematic diagram of a modified apparatus in which an untapped transformer, designed for the available voltages, is provided in the circuit shown in Figure l, and minor changes are otherwise made.

In Figure 1 is shown an induction heating coil in connected across the secondary winding I 2 of a power supply transformer I l. The primary winding it of this transformer i4- is provided with a plurality of taps. A low frequency preheating current source 24 is connected across an adjustable portion of said primary winding I6 through a first switch branch 18, a link second switch 32, a variable inductance 34 and the second branch 20 of said first switch. A condenser 36 is placed in parallel across said low frequency preheating current-supply 24. The link. switch 32 has a second position to bridge terminals 38 and 40 which may be used to place a suitable portion of the said primary winding l6 directly. across the low frequency preheating current source 24 through the first branch I8 of said first switch. With the link switch 32 in the latter described second position, thencondenser 36 and variable inductance 34 through the second branch 20 of said first switch are placedacross an adjustable portion of said primary winding IS.

The high frequency hardening current source 26 is connected across said primary winding l through a third switch 22 and a variable induc tance 28. This third switch 22 and the first switch combination l8. and 20. are/interlocked in such a manner that when the first switch combination i8 and29 is closed to apply the low frequency preheating current to the gear 30 undergoing heat treatment, the third switch 22 isopened. When the third switch 22is..closed to apply the high frequency hardening current to the gear 30 undergoing heat treatment, the firstswitch combination l8 and is opened.

The inductor coil Ill may be designed to accommodate gears of different sizes for heat treatment, or provision may be made in accordance with the skill of the art for replacing the inductor coil Ill with other inductor coils of different. sizes. A given. inductor. coil lllmay be employed to heat treat gears having different dimensions, provided the gear to be heat treated does not have external dimensions which too closel approach the internal. dimensions of such coil ID, or the external dimensions of the gear 30. are not too small relative to the internal, dimensions of the induction heating coil 10. This latter choice of induction heating coil l0. respecting the dimensions of the gear 30 to be heat treated is considered to. be well known in the skillof the art.

The apparatus shown in Fig. 2 is similar. to that shown in Figure 1, but an untapped transformer primary winding 44 is provided. This transformer: is designed. according to the available low frequency voltages. A- series inductance 28 is still used in the high frequency circuit. The link switch 32 described above with reference. to Fig. l, is no longer used, to result in a parallel connected low frequency circuit, including the series connected inductance 34 and capacitance 36.placed in parallel across the transformer primary winding 44.

The heat-treatment apparatus shown in Figure 1 operates to multiple frequency heat treat metallic gears which are individually placed in the single induction heating coil Ill. The first switch combination l8 and 20 is closed tobegin the heat-treatment operation. The link. second switch 32 is in its first positionas shown in-the figure. This energizes through firstswitch branch t8 a portion of the primary winding I6, which is serially connected through the second branch 20 of said first switch to a first variable. inductance 34. The latter variable inductance 34 may be adjusted depending upon the power requirements of the gear 30 undergoing heat treatment, as determined, for example, by its physical dimensions. When the link switch 32 is in the shown first position, a condenser 36- is parallel connected across the variable inductance 34 and primary winding portion Hi. This applies the low frequency current to preheat the gear 30 in the inductor coil Hl. One side of the low frequency power supply is grounded to complete the circuit.

The link switch 32 maybe moved to its second position bridging terminals 38 and 40 to place a. portion of the primary winding it directly across the low frequency power supply 24. This latter position of the link switch 32 places the condenser 36 and first variable inductor 34 through the; second branch 20 of the first switch across a second portion as shown of the primary winding IS. The taps on the primary winding lfi'permit the adjustment of the power actually applied to the gear in the inductor coil in through the secondary winding 12 over a relatively large range.

After the low frequency preheating power has been applied for asufliciently long period to. raise the temperature of the gear undergoing heat treatment to the desired value, the firstswitch combination l8 and 20 is opened, and the third switch 2'2 is closed to apply the high frequency hardening current. The time delay between the opening of the first switch combination l8 and 20 to shut off the low frequency preheat current, and the closing of the third switch 22 to apply the high frequency hardening current maybe chosen as desirable for the required heat treatment. However, the said switches are so interlocked that the low frequency preheating current and the high frequency hardening current are not concurrently applied to the gear 30 undergoing heat treatment. When the third switch 22. isclosed, the high frequency power supply isconnected across a portion of the. primary winding. l6 through a second variable inductor 28. The variable inductor 28 is provided to adjustthe: inductance of the circuit as seen by the power source. The various taps ofv the. primary winding l6 are provided to vary the power. input to the work. Inductance. removed from winding I6 is added by inductor 28. After the highfrequency hardening current has. been applied to the gear 30 for the predetermined time. intervaltc raise its temperature to that suitable. for hardening, the. thirdswitch22 isopened. The. power on-off" cycle is determined by keying the high frequency generator.

It is considered to be within the skill of the multiple frequency heat treatment art that the low frequency preheating treatment primarily heats the inner depths of the gear, and the high frequency hardening current primarily-heatsthe surface of the gear. The teachings of' our invention have in the main been employed for the contour hardening of metallic gears wherein only the contour of the gear is hardened andthe interior of the gear substantially retains its original hardness. However, for relatively small gears, the low frequency preheat current may heat up the whole of the gear body, and the high frequency hardening current will raise theetem, perature of a gear to a substantial depth intfrom its outer surface.

In the apparatus shown in Fig. 2, the maximum low frequency output would be obtained when the full voltage of the generator is applied to the transformer primary winding 44. Outiputs less. than maximum would be obtained by the series inductance 34 as in Figure 1. Series inductor 28 would be used with the high. frequency power sourceto makesmaAlchangps-in av input to the work. Large changes in high frequency power input to the work piece are made by changing the high frequency oscillator output. The latter can be accomplished b pulsing or changes in the plate voltage.

The circuits shown in Figs. 1 and 2 are intended for a number of gear hardening machines, each having similar circuits as shown, to be operated from respectively a single low frequency power source and a single high frequency power source. The switches are operated to properly time the heating cycle so this can be accomplished. One practical arrangement of our invention is to have six heat treatment machines operated from one high frequency oscillator and one motor-generator set. These machines would be properly synchronized so only one would request power from the high frequency oscillator at a given time. However, more than one of the machines would draw power from the motor-generator set because of the comparatively longer time duration of the respective low frequency heating cycles. The various circuit adjustments are provided so each of said six machines can at relatively the same time heat treat a metallic gear of a differ ent size and of different power requirements. Under these conditions, in the high frequency circuit the oscillator always sees substantially the same inductance, and in the low frequency circuit substantially the same generator output voltage is used for the various gears which require different power levels.

Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claim.

We claim as our invention:

In apparatus for the heat treatment of metallic objects by the successive application of multiple frequency currents from respectively a source of low frequency current and a source of high frequency current, the combination of a transformer having a primary winding and a secondary winding, an induction heating coil connected to said secondary winding, a first switch connected to said primary winding and adapted for connection between said primary winding and the source of low frequency current, a second switch connected to said primary winding adapted for connection between said primary winding and the source of hi h frequency current, an interlocking means provided between said switches so only one of said sources is connected to said primary winding at any given time, and a seriall connected variable inductance and variable capacitance in parallel with said primary winding.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,465,384 Wescoat Aug. 21, 1923 1,642,198 Gerth et a1 Sept. 13, 1927 2,189,819 Somes Feb. 13, 1940 2,202,758 Danneen et al May 28, 1940 2,276,643 Bates Mar. 17, 1942 2,321,189 Dravneek June 8, 1943 2,444,259 Jordan June 29, 1948 2,473,915 Slepian et al. June 21, 1949 2,482,493 King Sept. 20, 1949 2,564,906 Kincaid et al Aug. 21, 1951 2,590,546 Kincaid et a1 Mar. 25, 1952 2,623,176 Witsenburg et a1. Dec. 23, 1952 FOREIGN PATENTS Number Country Date 613,688 Great Britain Dec. 1, 1948 

